Method for production of carbon monoxide-reduced hydrogen-containing gas

ABSTRACT

A method for the oxidative removal of carbon monoxide from a hydrogen containing gas employing a catalyst for the selective oxidation of carbon monoxide is provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of prior U.S. patentapplication Ser. No. 10/847,857, filed May 19, 2004, which is acontinuation application of U.S. patent application Ser. No. 09/831,908,filed Jun. 19, 2001, which is the national stage application ofPCT/JP99/06535, filed Nov. 24, 1999. The parent application claimspriority to Japanese Application No. 10-335604, filed Nov. 26, 1998.

TECHNICAL FIELD

The present invention relates to a method for producing ahydrogen-containing gas through oxidative removal of carbon monoxidefrom a carbon monoxide-containing, hydrogen-containing gas.

BACKGROUND ART

Fuel cells for power generation do not so much pollute the environmentand their energy loss is low. Other advantages are that they can beinstalled in any desired site, and they are easy to increase, and areeasy to handle. Accordingly, fuel cells are specifically noticed thesedays. Various types of fuel cells are known that differ in the type offuel and electrolyte for them and in the operating temperature.Hydrogen-oxygen fuel cells (low-temperature-working fuel cells) in whichhydrogen serves as a reducing agent (active material) and oxygen (e.g.,air) serves as an oxidizing agent have been developed most of all, andwill be more and more popularized in future.

Various types of hydrogen-oxygen fuel cells are known that differ in thetype of electrolyte and the type of electrode therein. Typical examplesare phosphate-type fuel cells, KOH-type fuel cells, and solidpolymer-type fuel cells. In these fuel cells, especially those capableof operating at low temperatures such as solid polymer-type fuel cells,platinum (platinum catalyst) is used for the electrodes, and it iseasily poisoned with CO (carbon monoxide). Therefore, if CO of higherthan a predetermined level is in the fuel for them, the power-generatingcapability of the fuel cells is lowered. If the CO concentration in thefuel is too high, the fuel cells could not generate power at all, andthis is a serious problem.

Therefore, pure hydrogen is preferred for the fuel for these fuel cellshaving such a platinum-type electrode catalyst. From the practicalviewpoint, however, hydrogen-containing gas is generally used for them.This is obtained through steam reforming of various types of ordinaryfuels (for example, methane or natural gas (LNG); petroleum gas (LPG)such as propane, butane; various types of hydrocarbon fuels such asnaphtha, gasoline, kerosene, gas oil; alcohol fuels such as methanol;town gas, and other fuels for hydrogen production), for which publicsupply systems have been established. Therefore, a fuel-cellpower-generation system equipped with a fuel-reforming unit is now beingpopularized. However, the reformed gas generally contains a relativelyhigh concentration of CO in addition to hydrogen. Accordingly, it ismuch desired to develop a technique for converting CO in the reformedgas into CO₂ that is harmless to platinum-type electrode catalysts, tothereby reduce the CO concentration in the fuel for fuel cells. Forthis, it is desirable that the CO concentration in the fuel is loweredgenerally to at most 100 ppm, preferably to at most 10 ppm.

To solve the problem as above, a technique of utilizing shift reactionof the following formula (1) (aqueous gas shift reaction) has beenproposed for reducing the CO concentration in fuel gas(hydrogen-containing reformed gas) for fuel cells.

CO+H₂O═CO₂+H₂  (1)

However, reducing the CO concentration in fuel gas through only theshift reaction is limited, as the chemical equilibrium in the reactionis limited. In general, therefore, it is difficult to reduce the COconcentration in fuel gas to at most 1% through the shift reaction.

Accordingly, for further reducing the CO concentration in fuel gas,proposed is a method of introducing oxygen or an oxygen-containing gas(e.g., air) into fuel gas to thereby convert CO therein into CO₂.However, fuel gas contains a large amount of hydrogen. Therefore, whenCO in fuel gas is oxidized, then hydrogen therein is also oxidized, and,after all, the CO concentration in fuel gas could not be satisfactorilyreduced.

To solve the problem, a method of using a catalyst for selectivelyoxidizing only CO will be proposed in the process of introducing oxygenor an oxygen-containing gas into fuel gas so as to oxidize CO thereininto CO₂.

For CO oxidation catalysts, heretofore known are various catalysts ofPt/alumina, Pt/SnO₂, Pt/C, Co/TiO₂, hopcalite, and Pd/alumina. However,these catalysts are not well resistant to moisture, and their reactiontemperature range is low and narrow. In addition, their selectivity forCO is low. Fuel gas for fuel cells contains only a minor amount of CO ina majority of hydrogen. Therefore, if the catalysts are used forreducing the minor amount of CO in fuel gas to a lowered concentrationof at most 10 ppm, a large amount of hydrogen in fuel gas must besacrificed through oxidation.

Japanese Patent Laid-Open No. 201702/1993 discloses a method forproducing a CO-free, hydrogen-containing gas for automobile fuel cells,which comprises selectively removing CO from a hydrogen-rich,CO-containing gas. The catalyst used in this is Rh or Ru held on analumina carrier, but this is problematic in that it is applicable toonly a gas having a low CO concentration.

Japanese Patent Laid-Open No. 258764/1993 discloses a method ofprocessing a methanol-reformed gas (containing 20% by volume of CO₂ andfrom 7 to 10% by volume of CO, in addition to hydrogen) with an Fe—Crcatalyst to thereby reduce the CO concentration of the gas to 1% byvolume, followed by further reducing the CO concentration of the gasthrough methanation with a catalyst having a catalytic metal componentof Rh, Ni or Pd. In the method, CO still remaining in the processed gasis removed through plasma oxidation. The method provides a reformed gasfor solid polymer-type fuel cells, and the gas does not poison theplatinum catalyst for the electrode in the cells. However, as requiringa plasma generator, the method is problematic in that the reactionapparatus for it shall be large. In addition, the temperature formethanation in the method falls between 150 and 500° C. At such a highreaction temperature, not only CO but also CO, is methanated, and themethanation consumes a large amount of hydrogen in the gas. For thesereasons, the method is unsuitable for CO removal from ahydrogen-containing gas for fuel cells.

Japanese Patent Laid-Open No. 131531/1997 discloses a catalyst forremoving CO from a hydrogen-containing gas, and the catalyst comprisesruthenium and an alkali metal compound and/or an alkaline earth metalcompound held on a titania carrier. However, this discloses nothingabout a combination of titania and alumina for the carrier of thecatalyst. In addition, this suggests nothing about the fact that thecatalyst with a carrier of titania and alumina combined is significantlysuperior to the catalyst with a carrier of titania or alumina alone.

The present invention has been made in consideration of theabove-mentioned viewpoints, and its object is to provide a CO oxidationcatalyst which is effective for selectively oxidizing and removing COfrom a hydrogen-containing gas in a broad reaction temperature range,especially even at relatively high temperatures; to provide a method forproducing the catalyst; and to provide a method of using the catalystfor producing a hydrogen-containing gas, especially for producing ahydrogen-containing gas favorable to fuel cells.

DISCLOSURE OF THE INVENTION

We, the present inventors have assiduously studied, and, as a result,have found that a catalyst of ruthenium held on a carrier of titania andalumina is effective for selectively oxidizing and removing CO from ahydrogen-containing gas in a broad reaction temperature range. On thebasis of this finding, we have completed the present invention.

Specifically, the invention is summarized as follows:

(1) A CO oxidation catalyst of ruthenium held on a carrier of titaniaand alumina.

(2) A CO oxidation catalyst of ruthenium with an alkali metal and/or analkaline earth metal held on a carrier of titania and alumina.

(3) The CO oxidation catalyst of above (1) or (2), wherein the weightratio of titania to alumina falls between 0.1/99.9 and 90/10.

(4) The CO oxidation catalyst of above (2) or (3), wherein the alkalimetal is at least one selected from potassium, cesium, rubidium, sodiumand lithium.

(5) The CO oxidation catalyst of any of above (2) to (4), wherein thealkaline earth metal is at least one selected from barium, calcium,magnesium and strontium.

(6) A method for producing a CO oxidation catalyst of ruthenium with analkali metal and/or an alkaline earth metal held on a carrier of titaniaand alumina, which comprises applying a solution of ruthenium and asolution of an alkali metal and/or an alkaline earth metal to thecarrier.

(7) The method for producing a CO oxidation catalyst of above (6),wherein a mixed solution of ruthenium and an alkali metal and/or analkaline earth metal is applied to the carrier.

(8) A method for producing a CO-reduced, hydrogen-containing gas, whichcomprises selectively oxidizing carbon monoxide in a gas of essentiallyhydrogen, with oxygen in the presence of the catalyst of any of above(1) to (5) or the catalyst produced in the process of above (6) or (7).

(9) The method for producing a hydrogen-containing gas of above (8),wherein the gas of essentially hydrogen is obtained by reforming orpartially oxidizing a hydrogen-producing starting material.

(10) The method for producing a hydrogen-containing gas of above (8) or(9), wherein the hydrogen-containing gas produced is for fuel cells.

BEST MODES OF CARRYING OUT THE INVENTION

Embodiments of the invention are described hereinunder.

First described are the CO-removing catalyst (CO oxidation catalyst) ofthe invention, which is for removing CO from a gas of essentiallyhydrogen, and a method for producing the catalyst.

The carrier for the catalyst of the invention is composed of titania andalumina. As held on the carrier of titania and alumina, the catalyst ofthe invention is superior to the catalyst of ruthenium or ruthenium andan alkali metal compound and/or an alkaline earth metal compound held ona titania carrier or an alumina carrier, which is disclosed in JapanesePatent Laid-Open No. 131531/1997, in that its activity for CO oxidationand removal is high in a broader temperature range, especially atrelatively higher temperatures. In addition, as compared with thecatalyst held on a titania carrier, the catalyst of the invention heldon an alumina/titania carrier is easy to produce and shape, and has highmechanical strength and abrasion resistance, always keeping its highmechanical strength at any temperature at which it serves for COoxidation.

For producing the carrier composed of titania and alumina, employable isany method capable of producing the carrier composed of the two. Forexample, preferred is a method of mixing titania and alumina, or amethod of applying titania to shaped alumina (including alumina grainsand powder). For mixing titania and alumina, for example, employed is amethod of mixing titania powder with alumina powder or pseudo-boehmitealumina, along with water, then shaping the resulting mixture, dryingand calcining it. For shaping it, for example, the mixture may begenerally molded through extrusion. An organic binder may be addedthereto for improving the moldability of the mixture. Titania may bemixed with an alumina binder to give a good carrier of titania andalumina. Water may be added to a mixed solution of a titanium alkoxideand an aluminium alkoxide dissolved in a solvent such as alcohol. Inthis, the alkoxides are hydrolyzed, and the co-precipitated solid isshaped, dried and calcined in the same manner as above to give a carrierof titania and alumina. Preferably, the weight ratio of titania/aluminaof the carrier falls between 10/90 and 90/10.

On the other hand, titania may be adhered to shaped alumina, forexample, as follows. Titania powder (this may carry a catalytic metal,and the metal-carrying titania powder will be mentioned hereinunder),and optionally an organic binder and pseudo-boehmite alumina powder areadded to and well dispersed in an organic solvent. Shaped alumina isdipped in the resulting mixture (this is generally in the form ofslurry).

After the mixture has well penetrated into the shaped alumina and thetitania powder has adhered thereto, the shaped alumina is taken out ofthe mixture. With that, the shaped alumina is dried and calcined. Apartfrom the process, a titanium alkoxide or titanium tetrachloride, andshaped alumina are added to an alcohol, to which is added water tohydrolyze the titanium alkoxide or titanium tetrachloride. Then, theshaped alumina with titanium hydroxide having deposited thereon is driedand calcined. As in the titania-adhering methods, titania may be appliedto shaped alumina in any desired manner so that the shaped alumina cancarry titania. In the titania/alumina carrier thus produced according tothe method of adhering titania to shaped alumina, the weight ratio oftitania/alumina preferably falls between 0.1/99.9 and 50/50, morepreferably between 0.5/99.5 and 50/50, even more preferably between 1/99and 50/50. In the two methods mentioned above, the weight ratio oftitania/alumina of the carrier produced preferably falls between0.1/99.9 and 90/10, more preferably between 0.5/99.5 and 90/10, evenmore preferably between 1/99 and 90/10.

The starting material of alumina for the method of producing the carriermay be any and every one that contains aluminium atom(s). It includes,for example, aluminium nitrate, aluminium hydroxide, aluminiumalkoxides, pseudo-boehmite alumina, a-alumina, and γ-alumina.Pseudo-boehmite alumina, a-alumina and y-alumina are obtained fromaluminium nitrate, aluminium hydroxide and aluminium alkoxides.Depending on the method of producing the carrier, the starting materialeasy to use is selected.

The starting material of titania may also be any and every one thatcontains titanium atom(s). It includes, for example, titanium alkoxides,titanium tetrachloride, amorphous titania powder, anatase titaniapowder, and rutile titania powder. Amorphous titania powder, anatasetitania powder and rutile titania powder are obtained from titaniumalkoxides and titanium tetrachloride. Depending on the method ofproducing the carrier, the starting material easy to use is selected.

The carrier is composed of titania and alumina, but may contain anyother refractory inorganic oxide. For example, it may contain zirconiaand silica. The zirconia source may be any and every one that containszirconium atom(s), for which, for example, employable are zirconiumhydroxide, zirconium oxychloride, zirconium oxynitrate, zirconiumtetrachloride, and zirconia powder. Zirconia powder is obtained fromzirconium hydroxide, zirconium oxychloride, zirconium oxynitrate, andzirconium tetrachloride. The silica source may be any and every one thatcontains silicon atom(s), for which, for example, employable are silicontetrachloride, sodium silicate, ethyl silicate, silica gel, and silicasol. Silica gel is obtained from silicon tetrachloride, sodium silicate,ethyl silicate, and silica sol.

Next described is how to apply ruthenium to the carrier.

For applying ruthenium to the carrier, for example, a ruthenium salt isfirst dissolved in water or ethanol to prepare a catalyst solution. Theruthenium salt includes, for example, RuCl₃.nH₂O, Ru(NO₃)₃,Ru₂(OH)₂Cl₄7NH₃3H₂O, K₂(RUCl₅(H₂O)), (NH₄)₂(RuCl₅(H₂O), K₂(RuCl₅(NO)),RuBr₃nH₂O, Na₂RuO₄, Ru(NO)(NO₃)₃, (Ru₃O(OAc)₆(H₂O)₃)OAcnH₂O,K₄(Ru(CN)₆)nH₂O, K₂(Ru(NO₂)₄(OH)NO)), (Ru(NH₃)₆)Cl₃, (Ru(NH₃)₆)Br₃,(Ru(NH₃)₆)Cl₂, (Ru(NH₃)₆)Br₂, (Ru₃O₂(NH₃)₁₄)Cl₆H₂O, (Ru(NO)(NH₃)₅)Cl₃,(Ru(OH)(NO)(NH₃)₄)(NO₃)₂, RuCl₂(PPh₃)₃, RuCl₂(PPh₃)₄,(RuClH(PPh₃)₃)C₇H₈, RuH₂(PPh₃)₄, RuClH(CO)(PPh₃)₃, RuH₂(CO)(PPh₃)₃,(RuCl₂(cod))n, Ru(CO)₁₂, Ru(acac)₃, (Ru(HCOO)(CO₂)n, Ru₂I₄(p-cymene)₂.Of these, preferred are RuCl₃.nH₂O, and Ru₂(OH)₂Cl₄.7NH₃.3H₂O, as easyto handle.

For applying ruthenium to the carrier, the catalyst solution as abovemay be applied to the carrier in any ordinary method of dipping,co-precipitation or competitive adsorption. The condition for thetreatment may be suitably selected, depending on the method employed. Ingeneral, the carrier is kept in contact with the catalyst solution at atemperature falling between room temperature and 90° C., for 1 minute to10 hours.

The amount of ruthenium to be held on the carrier is not specificallydefined, but, in general, it preferably falls between 0.05 and 10% byweight, more preferably between 0.3 and 3% by weight of the carrier. Ifthe ruthenium content is smaller than the lowermost limit, the COconversion activity of the catalyst will be low; but if too large, theamount of ruthenium held on the carrier is excessive over the necessaryamount thereof, and the cost of the catalyst thereby increases.

After ruthenium has been applied to the carrier, it is dried. For dryingit, for example, employable is any known drying method of spontaneousdrying, evaporation to dryness, rotary evaporation, or air drying. Afterhaving been thus dried, this is calcined generally at 350 to 550° C.,preferably at 380 to 500° C., for 2 to 6 hours, preferably 2 to 4 hours.

Next described is how to apply an alkali metal and/or an alkaline earthmetal to the carrier. First described is how to apply an alkali metal tothe carrier. For the alkali metal, preferred are potassium, cesium,rubidium, sodium and lithium.

For applying the alkali metal to the carrier, a catalyst solution isprepared by dissolving an alkali metal salt in water or ethanol, andthis is applied to the carrier. The alkali metal salt includes K saltssuch as K₂B₁₀O₁₆, KBr, KBrO₃, KCN, K₂CO₃, KCl, KClO₃, KClO₄, KF, KHCO₃,KHF₂, KH₂PO₄, KH₅(PO₄)₂, KHSO₄, KI, KIO₃, KIO₄, K₄I₂O)₉, KN₃, KNO₂,KNO₃, KOH, KPF₆, K₃PO₄, KSCN, K₂SO₃, K₂SO₄, K₂S₂O₃, K₂S₂O₅, K₂S₂O₆,K₂S₂O₈, K(CH₃COO); Cs salts such as CsCl, CsClO₃, CsClO₄, CsHCO₃, CSI,CsNO₃, Cs₂SO₄, Cs(CH₃COO)Cs₂CO₃, CsF; Rb salts such as Rb₂B₁₀O₁₆, RbBr,RbBrO₃, RbCl, RbClO₃, RbClO₄, RbI, RbNO₂, Rb₂SO₄,Rb(CH₃COO), Rb₂CO₃; Nasalts such as Na₂B₄O₇, NaB₁₀O₁₆, NaBr, NaBrO₃, NaCN, Na₂CO₃, NaCl,NaClO, NaClO₃, NaClO₄NaF, NaHCO₃, NaHPO₃, Na₂HPO₃, Na₂HPO₄, NaH₂PO₄,Na₃HP₂O₆, Na₂H₂P₂O₇, NaI, NaIO₃, NaIO₄, NaN₃, NaNO₂, NaNO₃, NaOH,Na₂PO₃, Na₃PO₄, Na₄P₂O₇, Na₂S, NaSCN, Na₂SO₃, Na₂SO₄, Na₂S₂O₅, Na₂S₂O₆,Na(CH₃COO); and Li salts such as LiBO₂, Li₂B₄O₇, LiBr, LiBrO₃, Li₂CO₃,LiCl, LiClO₃, LiClO₄, LiHCO₃, Li₂HPO₃, LiI, LiN₃, LiNH₄SO₄, LiNO₂,LiNO₃, LiOH, LiSCN, Li₂SO₄, Li₃VO₄.

Described is how to apply an alkaline earth metal to the carrier. Forthe alkaline earth metal, preferred are barium, calcium, magnesium andstrontium.

For applying the alkaline earth metal to the carrier, a catalystsolution is prepared by dissolving an alkaline earth metal salt in wateror ethanol, and this is applied to the carrier. The alkaline earth metalsalt includes Ba salts such as BaBr₂, Ba(BrO₃)₂, BaCl₂, Ba(ClO₂)₂,Ba(ClO₃)₂, Ba(ClO₄)₂, BaI₂, Ba(N₃)₂, Ba(NO₂)₂, Ba(NO₃)₂, Ba(OH)₂, BaS,BaS₂O₆, BaS₄O₆, Ba(SO₃NH₂)₂; Ca salts such as CaBr₂, CaI₂, CaCl₂,Ca(ClO₃)₂, Ca(IO₃)₂, Ca(NO₂)₂, Ca(NO₃)₂, CaSO₄, CaS₂O³, CaS₂O₆,CaSO₃NH₂)₂, Ca(CH₃COO)₂, Ca(H₂PO₄)₂; Mg salts such as MgBr₂, MgCO₃,MgCl₂, Mg(ClO₃)₂, MgI₂, Mg(IO₃)₂, Mg(NO₂)₂, Mg(NO₃)₂, MgSO₃, MgSO₄,MgS₂O₆, Mg(CH₃COO)₂, Mg(OH)₂, Mg(ClO₄)₂; Sr salts such as SrBr₂, SrCl₂,SrI₂, Sr(NO₃)₂, SrO, SrS₂O₃, SrS₂O₆, SrS₄O₆, Sr(CH₃COO)₂, Sr(OH)₂.

For applying the alkali metal and the alkaline earth metal to thecarrier, the catalyst solution as above may be applied to the carrier inany ordinary method of dipping, co-precipitation or competitiveadsorption. The condition for the treatment may be suitably selected,depending on the method employed. In general, the carrier is kept incontact with the catalyst solution at a temperature falling between roomtemperature and 90° C., for 1 minute to 10 hours.

Ruthenium, the alkali metal and the alkaline earth metal may be appliedto the carrier in any order. If possible, these may be applied to thecarrier all at a time. Preferably, these are applied to the carrier allat a time. In case where these are applied to the carrier all at a time,a mixed catalyst solution containing ruthenium, an alkali metal and analkaline earth metal is prepared, and this is applied to the carrier.The method of applying these metals to the carrier all at a time ispreferred, as it is simple and the cost for catalyst production isreduced. In addition, the activity of the catalyst produced in themethod is high.

Apart from the methods of applying the active metals to the carrier thathas been formed previously, also employable is still another method offirst applying the active metals to titania, followed by adhering thetitania thus carrying the active metals to alumina to produce thecatalyst of the invention. Anyhow, the method for producing the catalystof the invention is not specifically defined, so far as the catalystproduced comprises ruthenium and other active metals held on atitania/alumina carrier.

The amount of the alkali metal and the alkaline earth metal to be heldon the carrier is not specifically defined, but, in general, itpreferably falls between 0.01 and 10% by weight, more preferably between0.03 and 3% by weight of the carrier. If the metal content is smallerthan the lowermost limit, the activity of the catalyst to selectivelyoxidize CO will be low; but if too large, the activity of the catalystto selectively oxidize CO will lower, and, in addition, the amount ofthe metals held on the carrier is excessive over the necessary amountthereof, and the cost of the catalyst thereby increases.

After the alkali metal and the alkaline earth metal have been applied tothe carrier, it is dried. For drying it, for example, employable is anyknown drying method of spontaneous drying, evaporation to dryness,rotary evaporation, or air drying. After having been thus dried, this iscalcined generally at 350 to 550° C., preferably at 380 to 500° C., for2 to 6 hours, preferably 2 to 4 hours.

The shape and the size of the catalyst thus produced are notspecifically defined. The catalyst may have any desired shape andstructure as in ordinary catalysts, for example, in any form of powers,spheres, granules, honeycombs, foams, fibers, cloths, plates, and rings.The method of shaping the catalyst is not specifically defined. Forexample, the catalyst may be molded through extrusion; or it may beadhered to honeycomb or ring substrates.

Next described is a method of using the catalyst for oxidizing carbonmonoxide in a gas of essentially hydrogen, with oxygen so as to producea CO-reduced, hydrogen-containing gas. The catalyst produced in themanner as above is generally calcined, and the active metals therein aregenerally in the form of their oxides. Before using it, the catalyst isreduced with hydrogen. For reducing it with hydrogen, in general, thecatalyst is exposed to hydrogen streams at a temperature falling between250 and 550° C., preferably between 300 and 530° C., for 1 to 5 hours,preferably for 1 to 2 hours.

In the presence of the thus-processed catalyst therein, oxygen is addedto a hydrogen-containing gas, which consists essentially of hydrogen andwhich contains at least CO, to thereby selectively oxidize CO in thegas. The CO oxidation method of the invention is favorable for selectiveCO removal from a gas of essentially hydrogen, which is obtained byreforming or partially oxidizing a hydrogen-producing material capableof being converted into a hydrogen-containing gas by reforming orpartially oxidizing it (this is hereinafter referred to as “reformedgas”), and is applied to production of a hydrogen-containing gas forfuel cells, to which, however, the invention is not limited.

The method of oxidative removal of CO from a gas of essentially hydrogenfor producing a hydrogen-containing gas for fuel cells is describedbelow.

1. Step of Reforming or Partial Oxidation of a Material for HydrogenProduction:

In the invention, CO in a reformed gas having been obtained by reformingvarious types of materials for hydrogen production is selectivelyoxidized with hydrogen in the presence of a catalyst to remove it fromthe gas, to thereby produce a hydrogen-containing gas of which the COcontent is fully reduced. The process of reformed gas production may beany desired one that has heretofore been carried out or proposed in theart for hydrogen production, especially for that in fuel cell systems,as will be described hereinunder. Therefore, in fuel cell systemsequipped with a gas-reforming unit, the reformed gas produced may beused directly in the invention as it is.

First described is how to reform or partially oxidize a material forhydrogen production. The material for hydrogen production is meant toindicate a material capable of being converted into a hydrogen-rich gasthrough its steam reforming or partial oxidation, and includes, forexample, hydrocarbons such as methane, ethane, propane, butane;hydrocarbon-containing materials such as natural gas (LNG), naphtha,gasoline, kerosene, gas oil, fuel oil, asphalt; alcohols such asmethanol, ethanol, propanol, butanol; oxygen-containing compounds suchas methyl formate, methyl tert-butyl ether, dimethyl ether; and alsovarious types of town gases, LPG, synthetic gases, and coals. The matterof selecting the material for hydrogen production herein from thosedepends on various related conditions such as the scale of fuel cellsystems and the material supply situation. In general, preferred aremethanol, methane or LNG, propane or LPG, naphtha or lower saturatedhydrocarbons, and town gases.

The technique of reforming or partial oxidation (this is hereinafterreferred to as “reforming technique”) includes, for example, steamreforming or partial oxidation, combination of steam reforming andpartial oxidation, autothermal reforming, and other reforming reactions.Of those, steam reforming is the most popular. To some specificmaterials, however, partial oxidation or other reforming techniques (forexample, thermal reforming such as pyrolysis, and other variouscatalytic reforming reactions such as catalytic decomposition and shiftreaction) may apply, if desired.

Also if desired, reforming reactions of different types may be combined.For example, steam reforming is generally accompanied by endothermicreaction, and it may be combined with partial oxidation that compensatesfor the part of endothermic reaction (the combination is autothermalreforming). As the case may be, CO having been side-produced in steamreforming may be reacted with H₂O in shift reaction, so that a part ofthe side product, CO is converted into CO₂ and H₂ to thereby reduce theCO content of the reformed gas. In that manner, steam reforming may becombined with any type of other reactions. If desired, after having beensubjected to partial oxidation in the absence of a catalyst or tocatalytic partial oxidation, the processed gas may be further subjectedto steam reforming in the latter stage of the process. In this case, theheat having been generated through the former-stage partial oxidationmay be directly used in the latter-stage steam reforming of endothermicreaction.

Steam reforming, one typical embodiment of reforming reaction isdescribed below.

In steam reforming, in general, the catalyst and the reaction conditionare so selected that the hydrogen absorption of the gas being processedcan be as large as possible. In this, however, it is difficult tocompletely inhibit side production of CO. Even if steam reforming iscombined with shift reaction, the CO content reduction in the reformedgas is limited. In fact, in steam reforming of hydrocarbons such asmethane, it is desirable that the condition is optimized for betterselectivity of the following reaction (2) or (3), to thereby increasethe hydrogen yield and retard side production of CO.

CH₄+2H₂O→4H₂+CO₂  (2)

CnHm+2nH₂O→(2n+m/2)H₂ +nCO₂  (3)

Similarly, in steam reforming of methanol, it is also desirable that thecondition is optimized for better selectivity of the following reaction(4):

CH₃OH+H₂O→3H₂+CO₂  (4)

Further, CO may be modified and reformed according to the shift reactionof formula (1) mentioned above. However, since the shift reaction isequilibrium reaction, a relatively large amount of CO still remains inthe reformed gas. Therefore, the gas reformed through the reaction (thisis the gas of essentially hydrogen that shall be processed in thepresent invention—the same shall apply hereinunder) shall contain CO₂,non-reacted steam and some CO, in addition to the majority of hydrogen.

Various types of catalysts are known effective for the reformingreaction mentioned above, and a desired one is selected from thesedepending on the type of the starting material to be processed and thetype of the reaction for reforming, and on the other reactionconditions. Some of the catalysts are mentioned below. For steamreforming of hydrocarbons and methanol, for example, Cu—ZnO catalysts,Cu—Cr₂O₃ catalysts, catalysts of Ni held on carrier, Cu—Ni—ZnOcatalysts, Cu—Ni—MgO catalysts, and Pd—ZnO catalysts are effective. Forcatalytic reforming or partial oxidation of hydrocarbons, for example,catalysts of Pt, Ni or Ru held on carrier are effective.

The reforming apparatus to be employed herein is not specificallydefined, and may be any and every one generally employed in ordinaryfuel cell systems. However, since most reforming reactions of steamreforming or decomposition are accompanied by endothermic reaction,generally preferred are reaction units and reactors of good heat supplythereto (for example, heat-exchangeable reaction units). Such reactionunits are, for example, multi-tubular reactors and plate-fin reactors.Regarding the mode of heat supply to these, for example, the reactorsmay be heated with a burner or a heating medium, or may be heatedthrough catalyst combustion for partial oxidation, to which, however,the invention is not limited.

The condition for reforming reaction shall be suitably determined, asvarying depending on the material to be processed, the type of reformingreaction, the catalyst used, the type of the reaction unit used, and thereaction mode in the unit. Anyhow, it is desirable that the reactioncondition is so selected that the conversion of the starting materialcan be the largest (preferably up to 100% or nearly 100%) and that thehydrogen yield can be the largest. If desired, the non-reactedhydrocarbon and alcohol may be recovered and recycled in the reactionsystem. Also if desired, the formed or non-reacted CO₂ and water may beremoved from the reaction system.

2. Step of Selective Oxidation (Conversion) and Removal of CO:

In the manner as above, obtained is a desired reformed gas which has alarge hydrogen content and from which the other components of thestarting material than hydrogen, such as hydrocarbons and alcohols havebeen fully removed.

In the invention, oxygen is added to the starting gas (reformed gas) ofwhich the majority is hydrogen and which contains a minor amount of CO,to thereby selectively oxidize (convert) the CO therein into CO₂. Inthis, therefore, the oxidation of hydrogen must be minimized as much aspossible. In addition, in this, the conversion of CO₂ having been formedor having existed in the starting gas into CO must be retarded (this isbecause the hydrogen in the starting gas may cause reverse-shiftreaction). Before used for the selective oxidation, the catalyst of theinvention is generally in a reduced condition. Therefore, if not, orthat is, if the catalyst is not reduced, it is desirable that thecatalyst is reduced with hydrogen before it is used for the selectiveoxidation. The catalyst of the invention produces a good result inselective oxidation and removal of CO not only from the starting gashaving a low CO₂ content but also from any others having a high CO₂content. In fuel cell systems, in general, used is a reformed gas havingan ordinary-level CO₂ content, or that is, a reformed gas having a CO₂content of from 5 to 33% by volume, but preferably a reformed gas havinga CO₂ content of from 10 to 25% by volume, more preferably from 15 to20% by volume.

On the other hand, the starting gas obtained through steam reforminggenerally contains steam, but the steam content of the starting gas tobe processed in the invention is preferably as small as possible. Ingeneral, the starting gas contains from about 5 to 30% of steam, and itssteam content on this level causes no problem in processing the startinggas with the catalyst of the invention.

Still another advantage of the catalyst of the invention is that notonly the CO content of the starting gas having a low CO content (of atmost 0.6% by volume) can be effectively reduced, but also the CO contentof any others having a relatively high CO content (of from 0.6 to 2.0%by volume) can also be effectively reduced.

In the hydrogen-containing gas production method of the invention, thecatalyst of the invention or the catalyst produced according to themethod of the invention is used. In this method, even when the startinggas has a high CO₂ content of 15% by volume or more, selectiveconversion and removal of CO from it is still possible even atrelatively high temperatures falling between 60 and 300° C. In this, theconversion and removal of CO from the starting gas is accompanied byendothermic reaction, like the side reaction, a hydrogen oxidationtherein. Therefore, the heat having been generated through the reactionin the method may be effectively recovered and recycled in fuel cellsfor increasing the power generation efficiency of the fuel cells.

In general, it is desirable that the oxygen gas to be added to thereformed gas is pure oxygen (O₂), air or oxygen-rich air. The amount ofthe oxygen gas to be added is preferably so controlled that the ratio ofoxygen/CO (by mol) falls between 0.5 and 5, more preferably between 1and 4. If the ratio is too small, the CO removal will be low; but if toolarge, it is unfavorable since the hydrogen consumption will increase.

The reaction pressure is not specifically defined. For fuel cells, ingeneral, it may fall between atmospheric pressure and 10 kg/cm²G, butpreferably between atmospheric pressure and 5 kg/cm²G. If the reactionpressure is set too high, the power for pressure elevation must belarge, which, however, is uneconomical. In particular, reaction pressurehigher than 10 kg/cm²G is undesirable as it must be controlled accordingto high-pressure gas regulations, and, in addition, such high reactionpressure is not safe as being critical for the possibility of explosion.

The reaction may be effected generally at a temperature not lower than60° C., preferably falling between 60 and 300° C. In such an extremelybroad temperature range, the reaction is stable and selective for COconversion. If the reaction temperature is lower than 60° C., thereaction speed will be low at such a low temperature, and if so, thedegree of CO removal (conversion) through the reaction will be lowwithin the practicable range of GHSV (gas hourly space velocity) for thereaction.

In general, it is preferable that the reaction is effected at GHSVfalling between 5,000 and 100,000 hr⁻¹. GHSV indicates the hourly spacevelocity of the gas supplied in the reactor, based on the standard-statevolume velocity of the gas supplied and passing through the catalystlayer and on the apparent volume of the catalyst layer. If GHSV is toosmall, a large amount of the catalyst is needed; but if too large, theCO removal will lower. Preferably, GHSV for the reaction falls between6,000 and 60,000 hr⁻¹. In this step of CO conversion and removal, the COconversion reaction is endothermic reaction, and this therefore elevatesthe temperature of the catalyst layer. If the temperature of thecatalyst layer is elevated too much, the selectivity of the catalyst forCO conversion and removal is generally lowered. Accordingly, it isundesirable that too much CO is reacted on a small amount of thecatalyst within a short period of time. To that effect, too large GHSVis often undesirable.

The reaction unit for the CO conversion and removal is not specificallydefined, and may be any and every one that satisfies the above-mentionedrequirements for the reaction. However, since the conversion reaction isendothermic reaction, preferred for it are reaction units or reactorsthat ensure easy removal of reaction heat from them for facilitatinggood temperature control therein. Concretely, for example, preferred areheat-exchangeable, multi-tubular or plate-fin reactors. As the case maybe, a coolant medium may be circulated in or around the catalyst layer.

Of the hydrogen-containing gas thus produced according to the method ofthe invention, the CO content is satisfactorily reduced, as so mentionedhereinabove. Accordingly, the gas does not poison or deteriorate theplatinum electrode catalyst in fuel cells, and therefore itsignificantly prolongs and increases the life and the power generationefficiency and capability of fuel cells. In addition, in the method ofproducing the hydrogen-containing gas of the invention, the heat havingbeen generated through the CO conversion reaction can be recovered.Moreover, even a hydrogen-containing gas having a relatively high COcontent can be well processed according to the method of the invention,and the CO content of the gas can be well lowered to a practicablelevel. In general, the CO content of the hydrogen-containing gas forfuel cells is preferably at most 100 ppm, more preferably at most 50ppm, even more preferably at most 10 ppm. According to the method of theinvention, it is surely possible to produce the hydrogen-containing gasof the preferred level, in a broad reaction condition.

The hydrogen-containing gas obtained in the invention is favorable tothe fuel for various types of H₂-combusting fuel cells, especially forthose at least having platinum (platinum catalyst) for the fuelelectrode (negative electrode), for example, low-temperature-workingfuel cells such as phosphate-type fuel cells, KOH-type fuel cells, andsolid polymer-type fuel cells.

When an oxygen-introducing unit and a CO conversion unit both to bedriven according to the method of the invention is installed in a spacebetween the reforming unit (in case where a modifying unit is after thereforming unit, this is considered as a part of the reforming unit) andthe fuel cell unit in a conventional fuel cell system; or when thecatalyst of the invention is used for the CO conversion and removalcatalyst in a fuel cell system equipped with an oxygen-introducing unitand a conversion reactor unit, and when the reaction condition for theCO conversion with the catalyst is controlled in the manner describedhereinabove, the fuel cell system thus constructed is superior to anyother conventional ones.

EXAMPLES

The invention is described more concretely with reference to thefollowing Examples, which, however, are not intended to restrict thescope of the invention.

Example 1

160 g of rutile-type titania (TiO₂, Ishihara Sangyo's CR-EL, having asurface area of 7 m²/g) and 59.7 g of pseudo-boehmite alumina powder(Shokubai Kasei Kogyo's Cataloid-AP) were mixed, and well kneaded withion-exchanged water in a kneader, and the water content of the resultingmixture was controlled to be enough for extrusion. Through an extruder,this was pelletized into columnar pellets having a diameter of 2 mm anda length of from 0.5 to 1 cm, and then dried in a drier at 120° C. for24 hours. Next, this was calcined in a furnace at 500° C. for 4 hours.This is carrier 1. The ratio by weight of titania/alumina of the carrier1 is 80/20.

10 g of the carrier 1 was metered, to which was applied a dippingsolution that had been prepared separately by adding 4.75 cc of ethanolto 5.25 cc of an ethanol solution of ruthenium chloride (containing0.952 g of Ru in 50 cc). This was heated at 60° C. to evaporate andremove ethanol, and calcined in a muffle furnace at 120° C. for 2 hoursand then at 500° C. for 4 hours. This is ruthenium-carrying carrier 1.

Next, 10 cc of an aqueous solution containing 0.0259 g of potassiumnitrate, which had been prepared separately, was applied to theruthenium-carrying carrier 1. This was heated at 60° C. to evaporate andremove water, and calcined in a muffle furnace at 120° C. for 2 hoursand then at 500° C. for 4 hours. This is catalyst 1. The composition ofthe catalyst 1 is shown in Table 1. The crash strength of the catalyst 1is 1.2 kg/mm, and this proves the durability of the catalyst 1 in use inordinary conditions.

Example 2

Carrier 2 having a ratio by weight of titania/alumina of 50/50,ruthenium-carrying carrier 2 and catalyst 2 were produced in the samemanner as in Example 1, for which, however, used were 100 g ofrutile-type titania (this is the same as in Example 1) and 149 g ofpseudo-boehmite alumina powder (this is the same as in Example 1) inplace of 160 g of rutile-type titania and 59.7 g of pseudo-boehmitealumina powder. The composition of the catalyst 2 is shown in Table 1.

Example 3

14.2 g of titanium tetraisopropoxide (TTIP, Wako Pure ChemicalIndustries special-grade chemical) was dissolved in 97 ml of isopropylalcohol, to which was added 5.25 g of diethanolamine, and stirred for 2hours. Next, a solution of 3.6 ml of isopropyl alcohol in 1.8 g of waterwas gradually added to it, and then stirred for 2 hours. 25 ml of theresulting solution was metered, to which was added 10 g of activatedalumina (Sumitomo Chemical's KHD24) that had been dressed to be 16 to32-mesh grains. This was left as it was for 1 hour, and the aluminagrains were taken out through filtration, and well washed with isopropylalcohol. The grains were calcined in a muffle furnace at 120° C. for 2hours and then at 500° C. for 4 hours. This is carrier 3. The carrier 3has titania adhering onto the solid grains of alumina (alumina grains).The ratio by weight of titania/alumina of the carrier 3 is 1/99.

10 g of the carrier 3 was metered, to which was applied a dippingsolution that had been prepared separately by adding 4.75 cc of ethanolto 5.25 cc of an ethanol solution of ruthenium chloride (containing0.952 g of Ru in 50 cc). This was heated at 60° C. to evaporate andremove ethanol, and calcined in a muffle furnace at 120° C. for 2 hoursand then at 500° C. for 4 hours. This is ruthenium-carrying carrier 3.

Next, 10 cc of an aqueous solution containing 0.0259 g of potassiumnitrate, which had been prepared separately, was applied to theruthenium-carrying carrier 3. This was heated at 60° C. to evaporate andremove water, and calcined in a muffle furnace at 120° C. for 2 hoursand then at 500° C. for 4 hours. This is catalyst 3. The composition ofthe catalyst 3 is shown in Table 1.

Example 4

3 g of activated alumina (Sumitomo Chemical's KHD24) that had beendressed to be 16 to 32-mesh grains was dipped in a titania dispersion of0.8 g of rutile-type titania (TiO₂, Ishihara Sangyo's CR-EL, having asurface area of 7 m²/g) and 0.3 g of pseudo-boehmite alumina powder(Shokubai Kasei Kogyo's Cataloid-AP) in 2 ml of a dispersion medium(ion-exchanged water/polyoxyethylene (10) octylphenyl ether (from WakoPure Chemical Industries)/acetylacetone=50/1/1 by volume), to therebymake titania adhere onto the alumina grains. The alumina grains weretaken out through filtration, washed and dried. The grains were calcinedin a muffle furnace at 120° C. for 2 hours and then at 500° C. for 4hours. This is carrier 4. The carrier 4 has titania adhering onto thesolid grains of alumina (alumina grains). The ratio by weight oftitania/alumina of the carrier 4 is 15/85.

3.84 g of the carrier 4 was metered, and dipped in 2 ml of an ethanolsolution of ruthenium chloride that had been prepared separately (thesolution contains 38.4 mg of Ru). This was heated at 60° C. to evaporateand remove ethanol, and calcined in a muffle furnace at 120° C. for 2hours and then at 500° C. for 4 hours. This is ruthenium-carryingcarrier 4.

Next, the ruthenium-carrying carrier 4 was dipped in 5 ml of an aqueoussolution of potassium nitrate that had been prepared separately (thiscontains 3.0 mg of K). With that, this was heated at 60° C. to evaporateand remove water, and calcined in a muffle furnace at 120° C. for 2hours and then at 500° C. for 4 hours. This is catalyst 4. Thecomposition of the catalyst 4 is shown in Table 1.

Example 5

Catalyst 5 of this Example is the ruthenium-carrying carrier 1 producedin Example 1. Its composition is shown in Table 1.

Comparative Example 1

10 g of rutile-type titania (TiO₂, Ishihara Sangyo's CR-EL, having asurface area of 7 m²/g) was dipped in 5.25 cc of an ethanol solution ofruthenium chloride that had been prepared separately (this contains0.952 g of Ru in 50 cc). This was heated at 60° C. to evaporate andremove ethanol, and calcined in a muffle furnace at 120° C. for 2 hoursand then at 500° C. for 4 hours. This is catalyst 6 (powdery catalyst).Its carrier is titania alone. The composition of the catalyst 6 is shownin Table 1. Before Ru was applied thereto, pelletizing the startingtitania into columnar pellets was tried through extrusion in the samemanner as in Example 1, but in vain.

Comparative Example 2

10 g of the catalyst 6 produced in Comparative Example 1 was metered, towhich was applied a dipping solution that had been prepared separatelyby dissolving 0.0259 g of potassium nitrate in 5.25 ml of ion-exchangedwater. This was heated at 60° C. to evaporate and remove water, andcalcined in a muffle furnace at 120° C. for 2 hours and then at 500° C.for 4 hours. This is catalyst 7 (powdery catalyst). Its carrier istitania alone. The composition of the catalyst 7 is shown in Table 1.

Comparative Example 3

A dipping solution that had been prepared separately by adding 4.75 ccof ethanol to 5.25 cc of an ethanol solution of ruthenium chloride(containing 0.952 g of Ru in 50 cc) was applied to 10 g of activatedalumina (Sumitomo Chemical's KHD24) that had been dressed to be 16 to32-mesh grains. This was heated at 60° C. to evaporate and removeethanol, and calcined in a muffle furnace at 120° C. for 2 hours andthen at 500° C. for 4 hours. This is catalyst 8. Its carrier is aluminaalone. The composition of the catalyst 8 is shown in Table 1.

Comparative Example 4

To 10 g of the catalyst 8 produced in Comparative Example 3, applied wasa dipping solution that had been prepared separately by dissolving0.0259 g of potassium nitrate in 10 ml of ion-exchanged water. This washeated at 60° C. to evaporate and remove water, and calcined in a mufflefurnace at 120° C. for 2 hours and then at 500° C. for 4 hours. This iscatalyst 9. Its carrier is alumina alone. The composition of thecatalyst 9 is shown in Table 1.

Example 6

10 g of the carrier 1 produced according to the process of Example 1 wasmetered, and dipped in a dipping solution that had been preparedseparately by dissolving 0.263 g of ruthenium chloride (containing38.03% of ruthenium metal) and 0.026 g of potassium nitrate. This wasdried at 60° C., and then calcined in air at 500° C. for 4 hours. Thisis catalyst 10. Its composition is shown in Table 1.

Example 7

10 g of the carrier 1 produced according to the process of Example 1 wasmetered, and sprayed with 2.0 cc of a dipping solution (this is the sameas in Example 6), with stirring under reduced pressure. This was driedat 120° C., and then calcined at 500° C. for 4 hours. This is catalyst11. Its composition is shown in Table 1.

Example 8

0.263 g of ruthenium chloride (containing 38.03% of ruthenium metal) and0.026 g of potassium nitrate were dissolved in 5.5 cc of water toprepare a dipping solution. 10 g of the carrier 3 produced according tothe process of Example 3 was metered, and sprayed with the dippingsolution, with stirring under reduced pressure. This was dried at 120°C., and then calcined at 500° C. for 4 hours. This is catalyst 12. Itscomposition is shown in Table 1.

Example 9

Ruthenium and potassium were applied to the carrier 1 produced accordingto the process of Example 1, in the manner mentioned below.

0.263 g of ruthenium chloride (containing 38.03% of ruthenium metal) wasdissolved in 2.0 cc of water to prepare a dipping solution. 10 g of thecarrier 1 was metered, dipped in the dipping solution, then dried at 60°C., and thereafter calcined in air at 500° C. for 4 hours. This isruthenium-carrying carrier 5.

0.026 g of potassium nitrate was dissolved in 2.0 cc of water to preparea dipping solution. The ruthenium-carrying carrier 5 was dipped in thedipping solution, and then dried at 60° C. This was calcined in air at500° C. for 4 hours. This is catalyst 13. Its composition is shown inTable 1.

Example 10

0.263 g of ruthenium chloride (containing 38.03% of ruthenium metal) wasdissolved in 2.0 cc of water to prepare a dipping solution. 10 g of thecarrier 1 was metered, and sprayed with the dipping solution withstirring under reduced pressure. This was dried at 120° C., and thencalcined in air at 500° C. for 4 hours. This is ruthenium-carryingcarrier 6.

0.026 g of potassium nitrate was dissolved in 2.0 cc of water to preparea dipping solution. The ruthenium-carrying carrier 6 was sprayed withthe dipping solution with stirring under reduced pressure, and thendried at 120° C. This was calcined in air at 500° C. for 4 hours. Thisis catalyst 14. Its composition is shown in Table 1.

Example 11 Comparative Example 5 Selective Oxidation of CO Gas

Before in use, each catalyst was dressed to be 16 to 32-mesh grains.Concretely, the catalysts 1, 2, 5, 10, 11, 13 and 14 each were ground,while the catalysts 6 and 7 each were shaped into tablets, using atablet-shaping machine, and then ground; and each catalyst powder wasdressed to be 16 to 32-mesh grains. The other catalysts were in the formof 16 to 32-mesh grains, and they were used as they were. The catalystwas packed into a fixed bed flow reactor, and hydrogen gas passedthrough it to reduce the catalyst at 500° C. for 1 hour.

A gas of essentially hydrogen was processed in the reactor for selectiveoxidation of CO therein, under the condition shown in Table 2. Thereaction temperature was varied in a range within which the COconcentration in the processed gas was reduced to at most 10 ppm. Theresults are given in Table 3. As in this, the catalyst activity wasevaluated on the basis of the temperature range within which the COconcentration in the processed gas was reduced to at most 10 ppm.

TABLE 1 Titania/Alumina Ratio in Carrier of Catalyst, and Amount ofMetal Held by the Carrier Method of TiO₂/Al₂O₃ (by Ruthenium PotassiumCatalyst Catalyst weight) (wt. %) (wt. %) Production Catalyst 1 80/201.0 0.1 Example 1 Catalyst 2 50/50 1.0 0.1 Example 2 Catalyst 3  1/991.0 0.1 Example 3 Catalyst 4 15/85 1.0 0.1 Example 4 Catalyst 5 80/201.0 0.0 Example 5 Catalyst 6 100/0  1.0 0.0 Co. Ex. 1 Catalyst 7 100/0 1.0 0.1 Co. Ex. 2 Catalyst 8  0/100 1.0 0.0 Co. Ex. 3 Catalyst 9  0/1001.0 0.1 Co. Ex. 4 Catalyst 10 80/20 1.0 0.1 Example 6 Catalyst 11 80/201.0 0.1 Example 7 Catalyst 12  1/99 1.0 0.1 Example 8 Catalyst 13 80/201.0 0.1 Example 9 Catalyst 14 80/20 1.0 0.1 Example 10

TABLE 2 CO Oxidation Condition Items Reaction Condition ReactionPressure atmospheric pressure Reaction Temperature 50 to 350° C. GasHourly Space Velocity 10,000 hr⁻¹ (GHSV) Composition of Gas Processed(vol. %) Hydrogen 74.4 Carbon Monoxide 0.6 Carbon Dioxide 15 Oxygen 2Nitrogen 8

TABLE 3 Result of CO Oxidation Reaction Temperature Catalyst Range (°C.)* Example 11 Catalyst 1 90-300 Catalyst 2 100-300  Catalyst 3 85-300Catalyst 4 110-270  Catalyst 5 85-280 Catalyst 10 70-300 Catalyst 1160-300 Catalyst 12 75-300 Catalyst 13 80-270 Catalyst 14 75-270 Comp.Example 5 Catalyst 6 50-250 Catalyst 7 95-200 Catalyst 8 110-250 Catalyst 9 90-250 *This is the reaction temperature range (° C.) withinwhich the CO concentration in the processed gas was reduced to at most10 ppm.

The catalysts carrying the same metal are compared in point of thehigh-activity temperature range for selective CO oxidation. As in Table3, the catalysts with the active metal on a carrier of titania andalumina combined (catalysts 1 to 5, and catalysts 10 and 14) are activein a broader temperature range than the catalysts with the active metalon a carrier of titania or alumina alone (catalysts 6 to 9). Inparticular, the former catalysts are active at high temperatures.Regarding their shapability including the mechanical strength of theshaped catalysts, the catalysts with the active metal held on a carrierof titania and alumina combined are superior to those with the activemetal held on a carrier of titania alone.

INDUSTRIAL APPLICABILITY

The method of the invention is effective for selective conversion andremoval of CO from a gas of essentially hydrogen within a broadtemperature range. When used in hydrogen-oxygen fuel cells, the methodprevents the platinum electrode (hydrogen electrode) from being poisonedby CO, and therefore prolongs the cell life and stabilizes the cells forpower generation.

1. A method for producing a CO-reduced, hydrogen-containing gas, whichcomprises selectively oxidizing carbon monoxide in a gas of essentiallyhydrogen, with oxygen in the presence of a CO oxidation catalystcomprising ruthenium with an alkali metal held on a carrier of titaniaand alumina, wherein the weight ratio of titania to alumina fallsbetween 1/99 and 15/85, and the amount of ruthenium falls between 0.3and 3% by weight of the carrier.
 2. The method for producing ahydrogen-containing gas as claimed in claim 1, wherein the gas ofessentially hydrogen is obtained by reforming or partially oxidizing ahydrogen-producing starting material.
 3. The method for producing ahydrogen-containing gas as claimed in claim 1, wherein thehydrogen-containing gas produced is for fuel cells.
 4. The method forproducing a CO-reduced, hydrogen-containing gas according to claim 1,wherein the alkali metal is at least one selected from the groupconsisting of potassium, cesium, rubidium, sodium and lithium.
 5. Themethod for producing a CO-reduced hydrogen-containing gas according toclaim 1, wherein the carrier of titania and alumina comprises titaniaadhering onto a shaped alumina.
 6. The method for producing a CO-reducedhydrogen-containing gas as claimed in claim 5, wherein the shapedalumina is solid grains or powder of alumina.
 7. The method forproducing a CO-reduced hydrogen-containing gas as claimed in claim 2,wherein the gas of essentially hydrogen is obtained by reforming orpartially oxidizing a hydrogen-producing starting material.
 8. Themethod for producing a CO-reduced hydrogen-containing gas as claimed inclaim 5, wherein the gas of essentially hydrogen is obtained byreforming or partially oxidizing a hydrogen-producing starting material.9. The method for producing a hydrogen-containing gas as claimed inclaim 4, wherein the hydrogen-containing gas produced is for fuel cells.